70 BULLETIN OF THE 



The attachment of the ooecium to the body wall of the mother stock 

 always remains small, as in Figure 99, and the embryo, in my experi- 

 ence, does not come in contact with it. 



The formation of the first polypide in Cristatella is preceded by 

 another process. Just as in the adult colony the inner layer of the 

 polypide does not arise by invagination of the ectoderm, but from the 

 stolouic cells lying at the base of the ectoderm (see Davenport, '90, 

 pp. 108, 109, Figs. 4 and 15), so too in the embryo. The first process 

 then must be the formation of the stolonic cells. Figure 101 shows at 

 the point marked sto. (which is at the pole of the embryo whence the 

 inner-layer cells originated) that certain of the cells of the ectoderm ap- 

 pear to be arching over a disk, containing about six cells in section, and 

 thus coming in contact with the cylinder of cells (*) which pi'ojects 

 from the neck of the ooecium. By a continuation of this process, the 

 central disk of cells gradually comes to lie below the general level 

 of the ectoderm, and to be cut off from contact with the neck of the 

 ooecium (Fig. 97, sto.). The position of the stolonic mass with refer- 

 ence to the neck of the polypide in this last figure must be considered 

 abnormal ; it is at any rate exceptional, as it lies at one side of the neck 

 of the ooecium, which does not, therefore, appear in this section. The 

 next later stage which I have found is shown in Figure 102. The sto- 

 lonic mass seen lying beneath the ectoderm in {'igure 97 has here 

 already given rise to a young polypide (^., ex.), and its area is increas- 

 ing in all directions by cell division {sto.). The beginning of a sec- 

 ond polypide is indicated on the right at 5^0. The ectoderm is seen 

 lying above this stolonic mass, and closely applied to the neck of the 

 ooecium (*). 



Neither at this nor at any subsequent stage have I been able to 

 detect in Cristatella any " gurtelformige Placenta" such as exists in 

 Pluraatella. I am therefore of opinion that the process of nutrition, 

 which is effected in Plumatella from the ooecium through its placenta, 

 is effected in the Cristatella larva by its attachment to the neck of the 

 ooecium. I am pleased to see that Jullien ('90, pp. 13, 14) has also 

 reached this conclusion in a paper which he has had the kindness to send 

 me. At a later stage, the embryo, or young colony, seems to become 

 detached from its intimate association with the neck of the ooecium, as 

 we see in Figures 95 and 103. 



Figure 103 represents a stage in which there are two well developed 

 buds, both shown in the section. There is, in addition, on another section, 

 one less developed. The stolon is seen passing oralward of these twc 



